In ring oscillators or wide-band digital controlled oscillators, the oscillation frequency is typically controlled within a predetermined frequency range by a large number of switchable capacitors that change the total capacitance of the oscillation frequency in steps. Since the oscillation frequency is typically a non-linear function of the total capacitance, a fixed step change of the total capacitance results in a corresponding step change of the oscillation frequency which decreases with frequency if the step change of the total capacitance is positive, or increases with frequency if the step change of the total capacitance is negative.
As a consequence, since the oscillation frequency cannot be accurately controlled, even a larger number of switchable capacitors is required to cover the full predetermined frequency range with acceptable resolution.